Prune changelogs after 8.18.6 release

docs/changelog/130336.yaml

@@ -1,5 +0,0 @@
-pr: 130336
-summary: "[EIS] Rename the elser 2 default model and the default inference endpoint"
-area: Machine Learning
-type: bug
-issues: []

docs/changelog/132638.yaml

@@ -1,5 +0,0 @@
-pr: 132638
-summary: Better error message for sequences with only one clause plus UNTIL
-area: EQL
-type: bug
-issues: []

docs/changelog/132646.yaml

@@ -1,5 +0,0 @@
-pr: 132646
-summary: Update EIS sparse and dense embedding max batch size to 16
-area: Machine Learning
-type: bug
-issues: []

docs/changelog/132766.yaml

@@ -1,10 +0,0 @@
-pr: 132766
-summary: Change `reporting_user` role to leverage reserved kibana privileges
-area: Authorization
-type: deprecation
-issues: []
-deprecation:
-  title: Deprecate the built-in `reporting_user` role.
-  area: Authorization
-  details: The `reporting_user` role is deprecated. Administrators should manage access to Kibana's reporting features via custom roles which grant the necessary privileges.
-  impact: This role will be removed in a future version. Administrators should migrate to custom roles to avoid interruption.